This invention relates to an improved pump mechanism for dispensing small aliquots of a liquid, such as a biological reagent. It may serve as part of an apparatus which dispenses a plurality of reagents to be dispensed in small volumes.
Current methods for dispensing reagents generally use pumps which require the priming of tubing lines leading into and out of a pump. When the pumping is finished, the tubing lines must be flushed before a different reagent can be pumped, lest cross-contamination of reagents occur. Because of the need for priming and clearing tubing lines, such types of pumps are not easily interchangeable.
Pumping systems using a syringe housing ("syringe pumps") are well known to those in the field. The liquid can then be accurately dispensed by applying a precise pressure on the plunger, usually by an electromechanical actuator. The distance that the plunger is depressed directly controls the amount of fluid to be dispensed. Such syringe pumps have two advantages: 1) the absence of tubing lines leading into and out of a pump which must be primed and flushed, and 2) the separation of the wetted components from the electromechanical controlling elements.
Such syringe pumps are useful in situations where repetitive dispensing of precise amounts of liquid are required. A drawback of such syringe pumps is that interchanging syringes on a single electromechanical actuator requires that the actuator mechanism be realigned with the position of the syringe plunger that is being inserted. In circumstances where the syringes need to be changed often in order to change the dispensed reagent, the need for repetitive manual intervention to align the electromechanical actuator with the position of the syringe plunger is a disadvantage.
A modified form of syringe pump is presented in U.S. Pat. No. 4,844,868 to Rokugawa and U.S. Pat. No. 5,232,664 to Krawzak et al. In those devices, liquid is drawn into a syringe from a reservoir through a check valve and then dispensed through a second check valve. Unfortunately, the increased complexity of sliding seals, valves with balls and springs and multiple parts to be assembled renders such designs relatively costly to manufacture. This is a particular disadvantage where the liquid dispenser is meant to be disposable.
U.S. Pat. Nos. 5,645,114 and 5,316,452 to Steven A. Bogen and Herbert H. Loeffler and assigned to the Assignee of this invention prevent a liquid dispensing pump comprising a metering chamber attached to a liquid reservoir. The reservoir is a syringe barrel, sealed at the top by a moving plunger. As liquid is dispensed, the plunger moves progressively deeper into the reservoir/syringe barrel. The plunger thereby serves to exclude air and prevent spillage of the liquid contained within the reservoir. The metering chamber comprises a flexible housing with two unidirectional duck-billed valves. As the housing is compressed, liquid is ejected out of the chamber through the lower valve. As the compression force is released, the flexible housing resumes its native (expanded) state, thereby drawing liquid into the housing from the reservoir.
By positioning a plurality of such liquid dispensers on a moving platform, a single electromechanical actuator can selectively dispense from a variety of dispensers. In this manner, the cartridge pumps are interchangeable.